全文获取类型
收费全文 | 4055篇 |
免费 | 290篇 |
国内免费 | 1077篇 |
专业分类
林业 | 592篇 |
农学 | 209篇 |
基础科学 | 616篇 |
1713篇 | |
综合类 | 1487篇 |
农作物 | 120篇 |
水产渔业 | 120篇 |
畜牧兽医 | 226篇 |
园艺 | 89篇 |
植物保护 | 250篇 |
出版年
2024年 | 33篇 |
2023年 | 141篇 |
2022年 | 213篇 |
2021年 | 214篇 |
2020年 | 219篇 |
2019年 | 246篇 |
2018年 | 171篇 |
2017年 | 241篇 |
2016年 | 277篇 |
2015年 | 257篇 |
2014年 | 255篇 |
2013年 | 259篇 |
2012年 | 358篇 |
2011年 | 352篇 |
2010年 | 322篇 |
2009年 | 272篇 |
2008年 | 241篇 |
2007年 | 268篇 |
2006年 | 221篇 |
2005年 | 189篇 |
2004年 | 125篇 |
2003年 | 122篇 |
2002年 | 80篇 |
2001年 | 56篇 |
2000年 | 41篇 |
1999年 | 41篇 |
1998年 | 41篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 20篇 |
1994年 | 30篇 |
1993年 | 10篇 |
1992年 | 19篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有5422条查询结果,搜索用时 15 毫秒
51.
52.
A video Monitor &Control system of tunnel based on DSP/BIOS is proposed,which is different from traditional video Monitor & Control system.It uses DSP to process image,and uses enhanced video input processor to qcquire image.This system satisfies all requirements of video supervision,and is a low cost system.It has a good application foreground.The system has been confirmed as a good veracity and practicability system through testing in the Zhongliang Mountain tunnel of Chongqing. 相似文献
53.
According to the requirements of communication power supply, such as high reliability, wide application and high availability, the authors raise a new remote control design for a multi-output power supply for communication equipment based on TCPIP protocol and embedded technology. Then the hardware design is given for the system is discussed based on Ethernet professional chip PRTL8019AS and related circuits. The firmware software design for the salve-computer based TCPIP technology, and the soft design of communieation and control for the master-computer are proposed based on Winsoek and MFC technology in detail A test machine is built to do the testing, the test results prove that the test machine works stably and well, satisfies the design rules and also provides a feasible method for the remote supervise in communication power supplier whose requirement includes remote supervise, no-people on duty and so on. 相似文献
54.
Aiming at the free-riding problem in team incentive, this paper designs a dynamic incentive mechanism based on implicit side contract with dynamic game theory by introducing the reasonable assumption that there is horizontal monitor in team production. The theoretic analysis indicates that the dynamic incentive mechanism, in which a strict group incentive compatibility contract is taken at the first stage and an individual incentive compatibility contract is taken at the second stage, can implement team cooperation uniquely in the general condition of risk aversion and stochastic production by only two stage repeated game. 相似文献
55.
Engineering designed mode has entered a new stage because of the development of network. New calculating system based on network appeared. By analyzing the common B/S architecture, this paper brings forward an reformative architecture based on Web services and ASP. NET in order to build the new mode of engineering calculation. It can fully implement the sharing of the resources and provide the engineering designers a wonderful calculating environment, and the working eifficiency of designers can be enhanced. 相似文献
56.
坝上生态农业工程生态效益监测与评价研究 总被引:15,自引:0,他引:15
利用遥感技术、地理信息系统和全球定位系统对河北坝上实施生态农业工程建设后的生态效益进行了监测与评价。定量描述了坝上生态环境的动态变化趋势,并对坝上生态农业工程的气候效益、土壤改良效益、农业水文生态效益进行了分析与评价。研究结果表明,通过工程治理,使农业生态系统的功能增强,结构合理,取得了显著的生态效益。 相似文献
57.
58.
结合喷雾机器人作业环境的要求,开发出基于客户端/服务器模式的远程控制平台.该平台实现了通过无线网络实时传输各类数据和控制命令,客户端再现了机器人的工作环境和状态.在此基础上进行了系统性能测试和轨迹测试.试验结果表明:为了保证良好的操控性,机器人所处区域信号强度必须大于30%,操作者根据反馈信息判断机器人是否偏离预定路径,并在偏离时给予有效的纠正,为解决喷雾机器人重喷、漏喷的问题提供了一种方法. 相似文献
59.
基于随机森林回归算法的小麦叶片SPAD值遥感估算 总被引:12,自引:0,他引:12
使用机器学习中的随机森林(RF)回归算法构建小麦叶片SPAD值遥感反演模型。以2010—2013年江苏地区试验点稻茬小麦3个生育期(拔节、孕穗、开花)的叶片为材料,结合我国自主研发的环境减灾卫星HJ-1对研究区域进行同步监测,分析了各生育期叶片SPAD值与8种植被指数间的相关性;以0.01水平下显著相关的植被指数作为输入参数,使用RF回归算法构建了每个生育期的小麦SPAD反演算法模型,即RF-SPAD模型,以支持向量回归(SVR)和反向传播(BP)神经网络算法构建的SVR-SPAD模型和BP-SPAD模型作为比较模型,以R2和均方根误差(RMSE)为指标,分析了每个生育期3个模型的学习能力和回归预测能力,结果表明:RF-SPAD模型在3个生育期都表现出最强的学习能力,R2和RMSE在拔节期分别为0.89和1.54,孕穗期分别为0.85和1.49,开花期分别为0.80和1.71;RF-SPAD模型在3个生育期的回归预测能力都高于BP-SPAD模型,高于或接近于SVR-SPAD模型,R2和RMSE在拔节期分别为0.55和2.11,孕穗期分别为0.72和2.20,开花期分别为0.60和3.16。 相似文献
60.
Objective management of grazing livestock production systems needs monitoring of forage production at the managerial unit level. Our objectives were to develop a system that routinely estimates forage above-ground net primary production (ANPP) at the spatial and temporal resolution required by farmers in the Pampas of Argentina, and to facilitate adoption of the system by end users as a managerial support tool. Our approach was based on the radiation use efficiency (RUE) logic, which proposes that ANPP is determined by the amount of photosynthetically active radiation absorbed by the canopy (APAR), and the efficiency with which that energy is transformed in above-ground dry matter (radiation use efficiency, RUE). APAR is the product of incoming photosynthetically active radiation (PAR) and the fraction absorbed by the canopy (fPAR). We estimated fPAR as a non-linear function of MODIS normalized difference vegetation index (NDVI). RUE was empirically estimated for the two principal forage resources of the region, yielding the following relations: ANPP = 0.6 × APAR + 12, (R2 = 0.86; p < 0.001; n = 18) for the upland sown pastures, and ANPP = 0.27 × APAR + 26, (R2 = 0.74; p < 0.001; n = 18) for the lowland naturalized pastures, with ANPP in g/m2/60 days and APAR in MJ/m2/60 days. The models were able to predict independent ANPP values with acceptable accuracy. Computational procedures were automated and run in a Relational Data Base Manager System that stored and managed all the information. The system is currently monitoring 212,794 ha in 83 farms and provides monthly ANPP values for the previous month and a history of the last 6 years. The data so generated show ANPP differences between the two major forage resources, considerable variability of a given month’s ANPP among years and paddocks, and contrasting among-farm differences in the efficiency of conversion of ANPP and forage supplements into beef production. The system was well accepted by end users who utilize it mainly for making near real time decisions according to last month ANPP, and explaining results of previous production cycles by incorporating ANPP as an explicative variable. However, there were differences among farmers in the degree of utilization, apparently related to the advisor’s attitude toward this new technology. Our results indicate that (1) forage production of large extensions can be monthly monitored at the paddock level by a small laboratory with capabilities in geographic information systems, and (2) advisors and farmers apply this information to their managerial decisions. 相似文献